The present invention relates to audio/video test and measurement, and more particularly to audio processing using a video rasterizer for displaying representative waveforms.
In a video instrument, such as a video waveform monitor or vectorscope, the video data is sampled at a high data rate, such as 27 MHz. Therefore a system clock is used in the instrument which has a frequency that is an integer multiple of the video data rate. For raster scan displays the video data is stored in a rasterizer. The contents of the rasterizer are readout for display at a rate such that the display is updated usually thirty times per second. In contrast audio data is sampled at a much lower rate than the video data rate, such as 48 kHz. To provide a waveform display of the audio data conventionally requires separate equipment having circuitry designed for audio data rates.
U.S. Pat. No. 5,485,199 by Bob Elkind et al entitled “Digital Audio Waveform Display on a Video Waveform Display Instrument”, issued Jan. 16, 1996, stores digital audio data in a small buffer memory and replaces bursts of video data through a digital-to-analog converter (DAC) running at the video sample rate. This super-clocking of the digital audio data to the video data rate works well with analog waveform display technology, since the DAC reconstruction filter interpolates the audio data as if it were at the digital sample rate. Therefore a single DAC and filter may be used to combine audio waveforms with video waveforms for simultaneous display of the interpolated digital data.
Prior digital audio waveform monitors generate a raster display by writing to a dedicated frame buffer read by a display controller at a display frame rate. A video waveform monitor generates frames for the display in a similar manner, but at a much higher clock frequency and pixel rate. To combine video and audio waveforms in the same platform has required separate buffers for building the audio and video histograms.
What is desired is a method of simultaneously displaying audio and video data using a shared display technique without discarding any data.